Optical magnification adjustment system and projection exposure device

ABSTRACT

An optical magnification adjustment system being capable of minutely correcting magnification. A first lens  1  of plano-convex is installed on the side of an object surface  5 , and a second lens  2  of concave-plano is installed on the side of a formed image surface  7 . By controlling the center space d between the first lens and the second lens, the image is enlarged or reduced. The radii of curvature R2 and R3 of the convex surface of the first lens and the concave surface of the second lens are respectively set according to the following equations.  
       R 2=(1− n 1)/φ2  
       R 3=( n 2−1)/φ3  
     where,  
     φ2 and φ3 represent optical power, and  
     n1 and n2 represent refraction indexes, respectively.

[0001] This application is a divisional of U.S. patent application Ser.No. 10/289,786 filed on Nov. 7, 2002, the disclosure of which is herebyincorporated by reference.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The invention relates to an optical magnification adjustmentsystem and a projection exposure device.

[0004] 2. Related Art

[0005] The photolithography method has been applied widely in variousfields, in which a prescribed pattern is photographically imprinted byan exposure device on the surface of a substrate coated withphotosensitive materials such as the photo resist, thereafter thepattern is formed on the substrate by etching process. Printed circuitboards are fabricated also by the exposure device in recent years. Witha demand for more and more high-speed, multi-functional, andminiaturized electronics devices, the printed circuit boards are alsorequired to be more and more multi-layered, dense, and microscopic.

[0006] Especially for building a multi-layered printed circuit board, anultra-high precision is required in aligning a pattern on each layerwith another when exposing the patterns.

[0007] In the tendency of the further miniaturization and multi-layeringof printed circuit boards as mentioned above, the expansion andcontraction of the board itself due to the difference between theexpansion coefficients of the copper foil and the epoxy resin composingthe printed circuit board can no longer be ignored.

SUMMARY OF THE INVENTION

[0008] It is an object of the present invention to provide an opticalmagnification adjustment system and a projection exposure device, thatare capable of adjusting the magnification for projecting an imageaccording to the expansion or contraction of a printed circuit board.

[0009] The preferred embodiment of the optical magnification adjustmentsystem of the present invention has two lenses—the first lens, beingplano-convex or plano-concave and having an optical power of φ2 asdefined by the equation below, and the second lens being concave-planoor convex-plano and having an optical power of φ3 as defined by theequation below—installed in a telecentric position on the side of theobject surface to be projected or on the side of the projected image inthe optical exposure system, and is capable of minutely adjusting thetotal system magnification of said optical exposure system.

φ3=−Φ(S1+e1)/d0

φ2=(Φ−φ3)/(1−d0φ3)

[0010] where,

[0011] Φ: Optical power of the optical magnification adjustment system,

[0012] S1: Distance from the first surface of the first lens to thesurface of an object 5 (photo mask surface),

[0013] d0: Center space between the two lenses, that satisfies themagnification β=1, and

[0014] e1=t1/n1 (where, t1: the center thickness of the first lens, n1:refractive index of the first lens)

[0015] By the system configuration described above, the magnification βmay be adjusted by increasing or decreasing the center space between thetwo lenses centering around d0, and therefore the magnification of theoptical exposure system may be minutely corrected for high-precisionenlargement or reduction of the projected image.

[0016] Further, with parallel planes of the same thickness as the totalcenter thicknesses of said two lenses being inserted, it is desired tohave the optical aberrations of said optical exposure system correctedin advance in accordance with its purpose.

[0017] By making said two lenses cylindrical, it is also possible tocorrect the magnification only in one direction of the image, eitherlongitudinally or laterally, by adjusting the center space d in the sameway as above.

[0018] In order to make achromatic condition, it is desired to set theAbbe numbers υ1 and υ2 of said two lenses in that the following equationwill be satisfied.

υ1/υ2≈φ2/φ3

BRIEF DESCRIPTION OF THE DRAWINGS

[0019]FIG. 1 is a schematic view of an embodiment of the opticalmagnification adjustment system of the invention.

[0020]FIG. 2 is a diagram explaining the principle of operation of theembodiment of the optical magnification adjustment system of theinvention.

[0021]FIG. 3 is a schematic view of an embodiment of the projectionexposure device of the invention.

[0022]FIG. 4 is a diagram explaining the principle of operation ofanother embodiment of the optical magnification adjustment system of theinvention.

[0023]FIG. 5 is a diagram explaining the principle of operation ofanother embodiment of the optical magnification adjustment system of theinvention.

[0024]FIG. 6 is a diagram explaining the principle of operation of yetanother embodiment of the optical magnification adjustment system of theinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0025] The invention will now be described in reference to the attacheddrawings.

[0026]FIG. 1 shows an optical magnification adjustment system A of theinvention being installed in a projection exposure device forfabricating printed circuit boards.

[0027] Rays of an exposure frequency that transmit through an objectsurface 5 to be projected, which is the mask surface of a photo mask,are minutely magnified or reduced by the optical magnificationadjustment system A in all directions or a predetermined directionaccording to a predetermined magnification, then are magnified orreduced by an optical exposure system 6 according to a regularprojection magnification, and finally form an image on an imageformation surface 7 of a printed circuit board. The projection exposuredevice will be described later in reference to FIG. 3.

[0028] The optical magnification adjustment system A comprises a firstlens 1 and a second lens 2, and its magnification may be adjusted byadjusting the distance between the first lens 1 and the second lens 2.Also, by employing cylindrical lenses as the first lens 1 and the secondlens 2, magnification or reduction in only one predetermined directionmay be realized.

[0029] This magnification may be set to compensate for the expansion orcontraction of the printed circuit board.

[0030] The optical magnification adjustment system A is supposed to beinstalled in a telecentric optical system. In this embodiment, it isinstalled in between the object surface 5 and the optical exposuresystem 6.

[0031]FIG. 2 shows the architecture of the optical magnificationadjustment system A in detail.

[0032] In this embodiment, the first lens 1 installed on the side of theobject surface is plano-convex and the second lens 2 on the side of theimage formation surface 7 is concave-plano. Also, the first lens may beplano-concave and the second lens 2 may be convex-plano.

[0033] By varying the center space d between the first lens 1 and thesecond lens 2, enlargement or reduction is made possible. Namely, byinitially setting the magnification to equi-multiple when the centerspace d is d0, the magnification may be increased or decreased byvarying the center space d around d0.

[0034] For this operation, the radii of curvature R2 and R3 of theconvex surface of the first lens 1 and the concave surface of the secondlens 2 are respectively set according to Equations 1 and 2 shown below.These equations are valid not only when the first lens 1 is plano-convexand the second lens is concave-plano, but also when the first lens 1 isplano-concave and the second lens 2 is convex-plano.

R2=(1−n1)/φ2  Equation 1

R3=(n2−1)/φ3  Equation 2

[0035] where,

[0036] φ2 and φ3 represent the optical powers, respectively, and

[0037] n1 and n2 represent the refractive indexes, respectively.

[0038] Equations 1 and 2 above are derived as follows.

[0039] As shown in FIG. 2, let R1 and R2 respectively represent theradii of the surface curvatures of the first lens 1, R3 and R4respectively the radii of the surface curvatures of the second lens 2,and φ1, φ2, φ3, and φ4 the optical powers (i.e., inverse of the focaldistance) of respective surfaces.

[0040] Further, let t1 and n1 respectively represent the centerthickness and the refractive index of the first lens 1, t2 and n2respectively the center thickness and the refractive index of the secondlens 2, and d the center space between the first lens 1 and the secondlens 2. Let S1 represent the distance between the first surface R1 ofthe first lens 1 and the object surface 5 (i.e., photo mask surface),and Sk the distance between the second surface R4 of the second lens 2and an image surface 50 (i.e., virtual image of the photo mask surface).

[0041] Letting Φ (i.e., inverse of the focal distance) represent thetotal power of the total optical magnification adjustment system, Φ maybe obtained by Equation 3, since the optical powers φ1 and φ4 are zerobecause R1 and R4 are plane.

Φ=φ2+φ3−dφ2φ3  Equation 3

[0042] In this instance, the magnification β of the opticalmagnification adjustment system is represented by Equation 4 inaccordance with the optical paraxial relationship.

β=−1/[Φ(S1+e1)+dφ3−1]  Equation 4

[0043] where,

[0044] e1=t1/n1, and

[0045] S1>0 when the object surface is on the left side of the firstlens.

[0046] Then, letting d be a standard space d0 when the magnification βbecomes equi-multiple (i.e., β=1), Equation 5 is derived from Equation 4and φ3 may be obtained.

φ3=−Φ(S1+e1)/d0  Equation 5

[0047] By substituting Equation 5 for Equation 3, φ2 may be obtained asfollows.

φ2=(Φ−φ3)/(1−d0φ3)  Equation 6

[0048] As φ2 and φ3 are determined, the radii of curvature R2 and R3 maybe respectively obtained from the refraction indexes of the two lenses,as shown in the following Equations 1 and 2.

R2=(1−n1)/φ2  Equation 1

R3=(n2−1)/φ3  Equation 2

[0049] The total power Φ of the optical magnification adjustment systemmay be set within the tolerance range of the telecentric degree of theoptical exposure system. In other words, the focal distance of theoptical magnification adjustment system may be assigned with a longfocal distance that falls within the tolerance range of thetelecentricity determined by the operation condition of the opticalexposure system.

[0050] The system will become a plano-convex+concave-plano combinationif a large negative (−) value is given to this focal distance, while itwill become a plano-concave+convex-plano combination if a large positive(+) value is given.

[0051] By obtaining Φ from φ2 and φ3 obtained above, and by substitutingΦ and φ3 for Equation 4, β may be obtained by the following equation.

β=−1/[(φ2+φ3−dφ2φ3)(S1+e1)+dφ3−1]  Equation 4′

[0052] where, e1=t1/n1.

[0053] As shown by this equation, the magnification β varies with thechange of the space d between the first lens 1 and the second lens 2,therefore the magnification β may be corrected by changing the space d.

[0054] Moreover, the magnification β of the total system including theoptical exposure system may also be corrected by adjusting the space d.

[0055] In this instance, the limit of the adjustment of magnification ofthe optical magnification adjustment system is established when thespace d between the first and second lenses equals 0, and themagnification (β=β0) may be derived from Equation 4′ above as follows.,

β0=−1/[(φ2+φ3)(S1+e1]  Equation 4″

[0056] In the above embodiment, the magnification varies at the samerate longitudinally and laterally with changing the space d between thetwo lenses because R2 and R3 of the first lens 1 and the second lens 2are based on a spherical surface. This system configuration will beeffective for multi-directionally correcting the magnification in orderto compensate for temperature variation in the optical exposure system.

[0057] Other than the above embodiments, it is also possible to apply acylindrical surface to the surfaces R2 and R3 of the first lens 1 andthe second lens 2, respectively.

[0058] In this case, the surfaces R2 and R3 become parallel planes inthe direction of the generator of the cylindrical surfaces, and themagnification in the direction of the generator becomes equi-multipleregardless of the space d between the first lens 1 and the second lens2. That is, the magnification in the generator direction does not vary.

[0059] On the other hand, in the direction lateral to the generator ofthe cylindrical surface, the above theoretical equations are valid asthey are. Therefore, the magnification may be changed only in thedirection lateral to the generator of the cylindrical surface. Namely,by changing the space d of the first lens 1 and the second lens 2,reduction or enlargement correction centering around the standard spaced0 (β=1) may be made possible.

[0060] Printed circuit boards, and other similar types of boards, mayexpand or contract only in one direction depending of the succeedingprocesses. Application of the cylindrical surfaces will be effective forcompensating for such directional expansion or contraction.

[0061] After the rays are transmitted through the optical magnificationadjustment system, the variation of the distance Sk between the imagesurface 50 of the object and the surface R4 may be expressed by Equation7 based on the paraxial relationship.

Sk=[(1−dφ3)S1+d]/[ΦS1−(1−dφ3)]  Equation 7

[0062] From this equation, the shift range of the standard space d maybe so determined that the difference to the distance Sk falls within thefocal depth tolerance of the exposure system when letting the standardspace d0 be the base.

[0063] Also, because the optical magnification adjustment system of theinvention is in convex-concave relationship, namely, it is a Fraunhofertype system, the optical magnification adjustment system can beachromatic. 99.

[0064] For example, if the refraction indexes of the wavelengths a and bto be achromatic are set to (n1a, n1b) and (n2a, n2b), by defining Abbenumbers υ1 and υ2 as shown in Equations 8 and 9,

υ1=(n1−1)/(n1a−n1b)  Equation 8

υ2=(n2−1)/(n2a−n2b)  Equation 9,

[0065] the system may be achromatic by appropriately selecting υ1 and υ2in Equation 10.

υ1/υ2≈φ2/φ3  Equation 10

[0066] As described above, minute magnification adjustment will berealized by adjusting the space between the lenses in the opticalmagnification adjustment system of the invention.

[0067] The projection exposure device shown in FIG. 1 will now bedescribed in detail in reference to FIG. 3.

[0068]FIG. 3 shows the process of receiving a printed circuit board Wcoated with photo resist from a preceding process, placing the board Won a stage 14 of the exposure device, imprinting a circuit patter, orthe like, depicted on a photo mask 11, and then transferring the board Wto the succeeding process.

[0069] The stage 14 is movable in the X, Y, Z directions and in θ degreeangle for alignment purpose.

[0070] The photo mask 11 is installed facing the board W, and a lightsource device 13 is installed facing the other side of the photo mask 11from the board W in that it irradiates rays of a predetermined frequencytoward the photo mask 11.

[0071] A projection lens 12 is placed in between the photo mask 11 andthe board W, in that a pattern on the photo mask 11 is projected ontothe board W by enlargement or reduction according to a prescribedmagnification.

[0072] In this embodiment, because the pattern on the photo mask 11 isprojected by the projection lens 12, the photo mask 11 may beminiaturized. Also by moving the stage 14, multiple patterns may beprojected on the board W.

[0073] Furthermore, although the photo mask 11 and the board W arearranged from top to bottom of the page, the arrangement is not limitedto it. They may also be arranged in the reverse direction, or the photomask 11 and the board W may be arranged vertically.

[0074] Also, the photo mask 11 may be moved instead of the board W, orboth of them may be moved.

[0075] As said optical magnification adjustment system A is installed inbetween said photo mask 11 and said projection lens 12, enlargement orreduction of the pattern can be corrected.

[0076] In the above embodiments, the magnification may be varied bychanging the center space d, but it is also possible to simplify thesystem configuration of the optical magnification adjustment system A bysetting the magnification to a constant.

[0077] An embodiment of such optical magnification adjustment system Ais described by FIGS. 4 and 5. This embodiment of an opticalmagnification adjustment system employs a pair of parallel planes 20. Asshown in FIGS. 4 and 5, the parallel planes 20 are bent according to acurve of secondary degree, thereby forming cylindrical surfaces,respectively. The parallel planes 20 are installed in between the photomask 11 and the projection lens 12 in the path of the rays, and thegenerator of the parallel planes 20 is aligned with a desired directionof enlargement or reduction.

[0078] By this system configuration, the parallel rays transmitted fromthe light source device 13 through the photo mask 11 enter the parallelplanes 20, and are magnified or reduced in only one direction beforebeing transmitted out, as shown in FIG. 4, therein the projectionmagnification is changed.

[0079] Therefore, by aligning the generator of the parallel planes 20 tothe longitudinal or lateral direction, enlargement or reduction in thelongitudinal or lateral direction of the board W becomes possible.

[0080] As shown in FIG. 5, by arranging the two parallel planes 20perpendicular to each other (i.e., their generators cross each other in90-degree angle), enlargement or reduction in the 90-degree directionmay be realized. By aligning the generators in the longitudinal andlateral directions of the board W in such system configuration,enlargement or reduction in both the longitudinal and lateral directionsof the board W may be realized.

[0081] In place of the parallel planes 20, cylindrical lenses 21 may beapplied, as shown in FIG. 6. By employing a combination of the twocylindrical lenses 21 like in the case of the parallel planes 20,enlargement or reduction in both the longitudinal and lateral directionsof the board W may be realized.

[0082] The adjusting magnifying power of the parallel planes 20 and thecylindrical lenses 21 may be determined according to the degree ofexpansion or contraction of the board W in the succeeding process.Namely, variation of the magnification may be realized by changing acylindrical lens of different power.

[0083] As mentioned above, it is desired to install the opticalmagnification adjustment system A with the optical aberrationscompensated in advance. Also, the optical magnification adjustmentsystem A is supposed to be positioned at a, so to speak, telecentricposition in the path of the rays.

[0084] As described above, said projection exposure device will allowsaid exposure to be rendered in accordance with the expansion orcontraction of sail board W.

1. An optical projection exposure device for imprinting a circuitpattern, or the like, on a printed circuit board, comprising: a photomask having a prescribed pattern, projection means for projecting saidphoto mask pattern onto said board, a light source device forirradiating exposure rays through said projection means for imprintingsaid photo mask pattern on said board, and an optical magnificationadjustment system installed in between said photo mask and said boardfor correcting the magnification of said pattern in at least onearbitrary direction.
 2. The device of claim 1 wherein: said opticalmagnification adjustment system has a first plano-convex orplano-concave lens with an optical power φ2, as defined by the equationbelow, and a second concave-plano or convex-plano lens with an opticalpower φ3, as defined by the equation below, both of which are installedin a telecentric position on the side of an object surface or on theside of an image in an optical exposure system, wherein the total systemmagnification of said optical exposure system may be minutely varied bychanging the space between said lenses, φ3=−Φ(S1+e1)/d0φ2=(Φ−φ3)/(1−d0φ3) where, Φ: Total optical power of said opticalmagnification adjustment system, S1: Distance from the first surface ofsaid first lens to said object surface (i.e., photo mask surface), d0:Center space of said two lenses, that satisfies a magnification β=1,e1=t1/n1 (t1: Center thickness of said first lens 1, n1: Refractionindex of said first lens 1).
 3. The device of claim 2 wherein: saidoptical exposure system has its optical aberrations corrected in advanceaccording to its purpose in a condition where parallel planes of theirtotal thickness equal to the total central thicknesses of said twolenses are inserted.
 4. The device of claim 2 wherein: said two lensesare cylindrical lenses.
 5. The device of claim 2 wherein: each of Abbenumbers υ1 and υ2 of said two lenses is set to satisfy the followingequation, υ1/υ2≈φ2/φ3.
 6. The device of claim 1 wherein: said opticalmagnification adjustment system corrects said magnification in at leastone direction, longitudinally or laterally of a board.
 7. The device ofclaim 1 wherein: said optical magnification adjustment system has atleast one cylindrical lens.
 8. The device of claim 1 wherein: saidoptical magnification adjustment system has parallel planes which arebent in accordance with a curve of secondary degree.
 9. The device ofclaim 1 wherein: said optical magnification adjustment system has one ofa cylindrical lens or a parallel plane bent according to a curve ofsecondary degree for correcting magnification in one direction, and oneof another cylindrical lens or another parallel plane bent according toa curve of secondary degree for correcting magnification in thedirection perpendicular to said one direction.
 10. The device of claim 1wherein: said optical magnification adjustment system is a telecentricoptical system.